A foil bearing has bearing surfaces formed of flexible thin films (foils) having low flexural rigidity, and is configured to support a load by allowing the bearing surfaces to be deflected. During the rotation of the shaft, fluid films (such as air films) are formed between a shaft and the bearing surfaces of the foils, and the shaft is supported in a non-contact state.
For example, in Patent Literatures 1 to 3 listed below, there is described a thrust foil bearing configured to support a shaft in the thrust directions. The thrust foil bearing includes a plurality of foils (top foils) provided at a plurality of positions in a circumferential direction on an end surface of a disc-like foil holder. In each of the foils, an end portion on an upstream side in a rotation direction of the shaft is fixed to the end surface of the foil holder, whereas an end portion on a downstream side in the rotation direction of the shaft is set as a free end. When the shaft is rotated, a thrust bearing gap is formed between a bearing surface of each of the foils and an end surface of a thrust collar (thrust runner) provided on the shaft. With fluid films in the thrust bearing gaps, the shaft is supported in thrust directions in a non-contact state.